\chapter{Introduction}\label{ch:cc_intro}

The coupled cluster program is designed for large-scale
correlated calculations of energies and properties using the
hierachy of coupled cluster models: CCS, CC2, CCSD and CC3.
The program offers almost the same options as the other
parts of the Dalton program for SCF and MCSCF wave functions.
It thus contains a wave function optmization section and a response function section
where linear, quadratic and cubic response functions are calculated.
For CC3 however, it is only possible to calculate the wave function and 
singlet excitation energies. At the moment molecular gradients are available 
only up to the CCSD level.  London orbitals have so far not been implemented 
for the calculation of magnetic properties. 
In the manual more details can be found about the specific implementations.

An additional feature of the program is that all levels of correlation
treatment have been implemented using integral-direct techniques making
it possible to run calculations using large basis sets.  


